Up to now, an ejector has been known as a depressurizing device that is applied to a vapor compression refrigeration cycle device. The ejector of this type has a nozzle portion that depressurizes a refrigerant, draws a gas-phase refrigerant which has flowed out of an evaporator due to a suction action of the ejection refrigerant ejected from the nozzle portion, mixes the ejection refrigerant with the suction refrigerant in a pressure increase part (diffuser portion), thereby being capable of increasing the pressure.
Accordingly, in a refrigeration cycle device (hereinafter, referred to as an ejector refrigeration cycle) including the ejector as the depressurizing device, a power consumption of a compressor can be decreased by the aid of a refrigerant boost action in the pressure increase part of the ejector, and a coefficient of performance (COP) of a cycle can be improved to a greater extent than a general refrigeration cycle device including an expansion valve or the like as a depressurizing device.
Further, Patent Document 1 discloses an ejector having a nozzle portion which depressurizes the refrigerant in two stages as the ejector that is applied to the ejector refrigeration cycle. In more detail, in the ejector of Patent Document 1, the refrigerant of a high pressure liquid-phase state is depressurized into a gas-liquid two-phase state in a first nozzle, and the refrigerant that has been put into the gas-liquid two-phase state is allowed to flow into a second nozzle.
With the above configuration, in the ejector of Patent Document 1, boiling of the refrigerant in the second nozzle is promoted to improve a nozzle efficiency as the overall nozzle portion, and the COP is to be further improved as the overall ejector refrigeration cycle.
In a general ejector, a diffuser portion (pressure increase part) is coaxially disposed on an extension line in an axial direction of a nozzle portion. In addition, Patent Document 2 discloses that a spread angle of the diffuser portion thus arranged is relatively reduced to enable an improvement in the ejector efficiency.
The nozzle efficiency means an energy conversion efficiency when a pressure energy of the refrigerant is converted into a kinetic energy in the nozzle portion. The ejector efficiency means an energy conversion efficiency as the overall ejector.
However, in the ejector of Patent Document 1, for example, a heat load of the ejector refrigeration cycle becomes low, and a pressure difference (a difference between a high pressure and a low pressure) between the pressure of a high-pressure side refrigerant and the pressure of a low-pressure side refrigerant in the cycle is reduced. As a result, the refrigerant is depressurized by the difference between the high pressure and the low pressure by the first nozzle, and most of the refrigerant may not be depressurized in the second nozzle.
In this case, an improvement in the nozzle efficiency by causing the gas-liquid two phase refrigerant to flow into the second nozzle is not obtained. As a result, the refrigerant may not be sufficiently pressurized by the diffuser portion.
On the contrary, it is conceivable that with the application of the diffuser portion having the relatively small spread angle disclosed in Patent Document 2 to the ejector of Patent Document 1 to improve the ejector efficiency, the refrigerant is sufficiently pressurized in the diffuser portion even in the low load of the ejector refrigeration cycle.
However, when the diffuser portion of this type is applied, a length of the nozzle portion in the axial direction becomes longer as the entire ejector. As a result, a volume of the ejector becomes unnecessarily longer in the normal load of the ejector refrigeration cycle.